Negative expectations can increase pain, but can they promote the development of central sensitization? This study used an inert treatment and verbal suggestions to induce expectations of increased high-frequency electrical stimulation (HFS)-induced pain and assessed their effects on pain ratings during HFS and HFS-induced pinprick hypersensitivity. Fifty healthy volunteers were randomly allocated to either a control group (N = 25) or a nocebo group (N = 25). Participants in both groups received a patch containing water on the right forearm. The nocebo group was told that the patch contained capsaicin that sensitized their skin, while the control group was told that the patch contained water that had no effect on skin sensitivity. Before and after patch attachment, single electrical stimuli were delivered to the area of the patch to measure the perceived intensity to these stimuli. After patch removal and after the participant rated expected pain and fear for HFS, HFS was delivered to the same skin site, followed by the assessment of pinprick sensitivity. The nocebo group rated the perceived intensity for the single electrical stimulus after removal of the patch as more intense compared with the control group, indicating that our manipulation worked. Yet, this effect did not transfer to expected pain for HFS, nor did it affect pain intensity ratings during HFS. HFS increased pinprick sensitivity but no group differences were found. Because of the lack of differences in expected pain and pain intensity ratings for HFS between groups, no firm conclusions can be drawn regarding their effect on pinprick hypersensitivity. PERSPECTIVE: This study shows that sham treatment combined with verbal suggestions induces a nocebo effect but does not necessarily change expectations and experience of upcoming pain.

AIMS: Low back pain (LBP) is a common health problem in pre-professional dancers which could hamper the dancers’ professional career. However, pre-professional dancers are not often studied, although they may have their own pain perceptions and coping strategies towards LBP. Considering the biopsychosocial nature of LBP, it is important to increase the understanding of these perceptions and coping strategies. The aim of this qualitative research study was to explore the dancers’ perceptions about LBP and their coping strategies when they suffered from LBP. METHODS: Eighteen pre-professional dancers with and without LBP from different dance schools in Belgium were included in this study. Participants were invited for an in-depth online video interview. These in-depth interviews were based on a topic list. Afterwards, the interview transcripts were analyzed thematically. RESULTS: Two primary themes emerged from the data: 1) perceptions of LBP and 2) coping strategies which dancers applied when they suffered from LBP. The perceptions about LBP were related to two different themes: “it’s all about the body” and “it’s all about the psychosocial and contextual factors.” In addition, the coping strategies were divided into “active coping strategies” and “passive coping strategies,” whereas the most popular coping strategies were stretching exercises and passive coping strategies such as massages or heating cream. CONCLUSION: Although LBP has clearly been shown to be a biopsychosocial phenomenon, this qualitative study showed that dancers mainly considered biomedical factors as contributing factors to LBP. Additionally, instead of relying on coping strategies aimed at directly improving pain or trying to treat LBP on the basis of a single-cause diagnosis, it is important to consider the biopsychosocial origin of LBP in the management plans.

This study investigated whether expecting more pain increases high-frequency electrical stimulation (HFS)-induced pain and pinprick hypersensitivity. Fifty healthy volunteers were randomly allocated to either a control group (N=25) or a nocebo group (N=25). Participants in both groups received a patch containing water on the right forearm. The nocebo group was told that the patch contained capsaicin that sensitized their skin, while the control group was told that the patch contained water that had no effect on skin sensitivity. Before and after patch attachment, single electrical stimuli were delivered to the area of the patch to measure the perceived intensity to these stimuli. After patch removal, and after the participant rated expected pain and fear for HFS, HFS was delivered to the same skin site. To assess changes in pinprick sensitivity, pinprick stimuli were delivered before and after HFS. The nocebo group rated the perceived intensity for the single electrical stimulus after removal of the patch as more intense compared to the control group, indicating that our manipulation worked. Yet, this effect did not transfer to expected pain for HFS, nor did it affect pain intensity ratings during HFS. HFS increased pinprick sensitivity but no group differences were found. Because of the lack of differences in expected pain and pain intensity ratings for HFS between groups, no firm conclusions can be drawn regarding their effect on pinprick hypersensitivity. Nevertheless, exploratory analyses showed a significant and moderate correlation between the expected pain for HFS and the actual pain intensity reported during HFS.

Temporomandibular disorders (TMD) include a group of musculoskeletal disorders that may involve increased responsiveness of nociceptive neurons in the central nervous system (ie, central sensitization). To test this hypothesis further, this study examined whether, as compared with healthy subjects, patients with chronic TMD have a greater propensity to develop secondary mechanical hyperalgesia-a phenomenon that can be confidently attributed to central sensitization. In this case-control study, we assessed the area of secondary mechanical hyperalgesia induced experimentally by delivering high-frequency electrical stimulation (HFS) to the volar forearm skin in 20 participants with chronic TMD and 20 matched healthy controls. High-frequency electrical stimulation consisted in 12 trains of constant-current electrical pulses (5 mA) delivered at 42 Hz. The area of secondary mechanical hyperalgesia was evaluated 30 minutes after applying HFS. The area of secondary mechanical hyperalgesia induced by HFS was on average 76% larger in the chronic TMD group (M = 67.7 cm(2), SD = 28.2) than in the healthy control group (M = 38.4 cm(2), SD = 14.9; P = 0.0003). Regarding secondary outcomes, there was no group difference in the intensity of secondary mechanical hyperalgesia, but allodynia to cotton after HFS was more frequent in the chronic TMD group. To the best of our knowledge, this is the first study to show that individuals with chronic TMD have an increased propensity to develop secondary hyperalgesia in a site innervated extratrigeminally. Our results contribute to a better understanding of the pathophysiology of chronic TMD.

Background Conflicting results exist between somatosensory profiles of patients with temporomandibular myalgia (TMDm). The objective of this review was to examine whether adults with TMDm show altered responses to dynamic quantitative sensory tests compared with healthy controls. Methods We searched five electronic databases for studies, excluding those without suitable controls or where TMDm was associated with confounding non-musculoskeletal disorders. Risk of bias was assessed with the SIGN case-control study checklist. Findings were structured around dynamic quantitative sensory tests and their localization. Where possible, we performed meta-analysis with a random inverse variance model to compare patients with TMDm and healthy controls. Statistical heterogeneity was estimated with Chi(2) test and inconsistency index, I-2. Results We extracted data from 23 studies comprising 1284 adults with chronic TMDm and 2791 healthy controls. Risk of bias was assessed as high for 20 studies. Mechanical temporal summation, the most studied phenomenon (14 studies), is increased in the upper limb of patients with TMDm (SMD = 0.43; 95% CI: .11 to .75; p = .009) but not in the jaw area (p = .09) or in the cervical area (p = .29). Very little evidence for altered thermal temporal summation (five studies), conditioned pain modulation (seven studies), exercise-induced hypoalgesia (two studies), placebo analgesia (two studies), stress-induced hypoalgesia (one study) and offset analgesia (one study) was found. Discussion A major limitation of this review was the risk of bias of included studies. Future studies would benefit from following methodological guidelines and consideration of confounding factors.

BACKGROUND:Temporomandibular disorders (TMD) are characterised by complex symptomatology and their assessment can be enhanced using pain drawings (PD). OBJECTIVES:To evaluate the location and extent of pain in people TMD using digital PD, and to explore their association with clinical features. Reliability of pain extent and pain location using PD was also assessed. METHODS:Forty volunteers with TMD completed two consecutive digital PDs. Clinical features were captured from self-reported questionnaire. Additionally, secondary hyperalgesia was measured using the pressure pain threshold (PPT). The correlation between pain extent and clinical features was investigated using Spearman rank correlation coefficients. Reliability of pain extent was evaluated using intraclass correlation coefficient (ICC) and Bland-Altman plots. The Jaccard index was computed to assess the reliability of pain location. RESULTS:Analysis of the PDs indicated that people with TMD commonly experience pain in other body regions including the neck, the shoulder and the low back. Except for PPT and pain catastrophising, all other clinical features were significantly correlated with pain extent. The ICCs of pain extent for all body charts were very high (ICCs 95% CI from 0.73 to 0.96), and Bland-Altman plots showed mean biases close to zero with narrow limits of agreement. The reliability of pain location was also supported by Jaccard index mean scores above 0.68. CONCLUSIONS:People with TMD showed widespread pain, and pain extent was associated with pain intensity, neck and headache-related disability, depression, anxiety, hyperventilation and central sensitivity. The reliability of measuring pain extent and pain location was confirmed.

Synopsis Central sensitization is (1) increasingly interpreted as central nervous system hyperexcitability that accounts for a general increase in sensitivity, and (2) used to explain a variety of pain and nonpain symptoms. In this commentary, we argue that such a broad interpretation might not be clinically useful because it fails to distinguish one patient from another based on pathophysiological mechanisms and does not facilitate tailored treatment. We recommend that clinicians use a person-centered approach when assessing and managing patients, considering the different interacting processes/mechanisms that can contribute to a patient's clinical presentation. J Orthop Sports Phys Ther 2021;51(5):204–206. Epub 15 Mar 2021. doi:10.2519/jospt.2021.10340

BACKGROUND An increasing number of studies are focusing on secondary hyperalgesia to better understand central sensitization, as this phenomenon may play an important role in persistent pain. Recent studies have shown that, compared to the classical high frequency stimulation protocol (HFS) at 100 Hz, a protocol using 42 Hz stimulation induces a more intense and a larger area of secondary hyperalgesia (SH). OBJECTIVES The aim of this study was to investigate the within- and between-session reliability of SH induced by this optimized HFS protocol. METHODS Thirty-two healthy subjects received HFS to their volar forearm in two sessions, separated by at least two weeks. SH was assessed by measuring the area size of increased sensitivity to pinprick stimuli after applying HFS, the sensitivity to pinprick stimuli after applying HFS, and the change in pinprick sensitivity after vs. before HFS. Assessments were made before HFS, and 30, 35 and 40 minutes after HFS. Relative and absolute reliability were analyzed using intra-class correlation coefficients (ICCs), coefficients of variation (CVs), standard error of means (SEMs) and the minimum detectable changes (MDCs). RESULTS The area of SH showed good to excellent within-session and between-session relative reliability (ICCs > 0.80), except for the change in pinprick sensitivity, which showed close to poor between-session relative reliability (ICC=0.53). Furthermore, measures of absolute reliability generally demonstrated large between-subject variability and significant fluctuations across repeated measurements. CONCLUSIONS HFS-induced hyperalgesia is suitable to discriminate or compare individuals but it may not be sensitive to changes due to an intervention.

AIMS:Circus is a physically demanding profession, but injury and help-seeking rates tend to be low. This qualitative interview study explored the perceptions and beliefs about injury and help-seeking of circus artists.METHODS:Ten professional circus artists (5 males, 5 females; mean age 33 yrs, range 27-42) were enrolled. Individual, semi-structured interviews were conducted until data saturation of themes was reached. Data were analysed thematically.FINDINGS:Four themes were identified: 1) the injured artist; 2) professionalism; 3) circus life; and 4) artists' experience of healthcare. Most participants described the circus as central to their lives, and injuries had wide-ranging psychosocial consequences. Injury adversely affected participants' mood and threatened their identity. Situational and personal factors (e.g., the belief that pain was normal) pushed participants to use adaptive strategies to perform when injured. Continuous touring and financial constraints affected help-seeking. Easy access to healthcare was rare and participants often self-managed injuries. Experiences of healthcare varied, and participants desired flexible and accessible approaches to prevention and injury management. A modified version of the integrated model of psychological response to injury and rehabilitation process and the concept of identity provided a framework to understand participants.CONCLUSION:Injuries had extensive negative consequences. Work schedules, financial factors, employer support, the artist's perception of the importance of the show, and the relationship between circus and identity influenced injury management and help-seeking. Injury prevention and management strategies could be optimised by developing centres of expertise, online resources, and better regulations of the profession.

Background: Pain drawings (PDs) are frequently used to assess patients with pain and are included within the Diagnostic Criteria for Temporomandibular Disorders (DC-TMD). The PD helps clinicians to identify the presence of widespread pain or other regional pain conditions. Purpose: This study examines the association between pain extent extracted from the PD and clinical features in patients with temporomandibular disorders (TMD). Furthermore, the test-retest reliability of quantifying pain extent and pain location from five body diagrams representing different body regions was assessed (mouth, right and left profile of the head, and dorsal and frontal view of the full body). Methods: Forty patients with painful TMD, assessed by the Diagnostic Criteria for Temporomandibular disorders (DC-TMD - Axis 1), participated. Each patient shaded two consecutive electronic PDs using a digital tablet. A customized software quantified the pain extent for each body chart and presented the pain location according to standardized anatomical grids. Clinical features were evaluated. Secondary hyperalgesia was assessed via the pressure pain threshold over the tibialis anterior muscle of the right leg. Questionnaires were also completed by the participants including the Central Sensitization Inventory to screen for the presence of central sensitization, the Pain Catastrophizing Scale to assess pain catastrophizing, the SF-36 to assess quality of life, the brief pain inventory (short form) to evaluate the severity of a patient´s pain and the impact of this pain on the patient´s daily functioning, the Hospital Anxiety and Depression Scale to evaluate the level of anxiety and depression, the Nijmegen questionnaire to assess hyperventilation, the Neck Disability Index to assess neck disability and the HIT-6 questionnaire to assess adverse headache impact. The reliability of pain extent was evaluated using Intraclass Correlation Coefficients (ICC) and Bland Altman plots, while reliability of pain location was evaluated using the Jaccard index. Spearman correlation coefficients were computed to reveal correlations between pain extent and clinical features. Results: Significant correlations were observed between pain extent and all measured clinical features except for secondary hyperalgesia and pain catastrophizing. The ICCs for pain extent were very high ranging from 0.85 to 0.94. The Bland Altman showed a mean difference close to zero for the five PDs showing good reliability for pain extent. The Jaccard index ranged from 0.68 to 0.80 suggesting a good reliability for pain location. Conclusion(s): Digital pain drawings are a reliable tool to quantify pain extent and pain location in people with painful TMD. Furthermore, the extent of pain perceived is associated with a number of clinically relevant features highlighting the relevance of the PD when evaluating patients with TMD. Implications: Clinicians can reliably assess the pain extent and pain location of TMD patients with a digital tablet and PD acquisition software. Measures of pain extent can facilitate clinicians in the assessment and the monitoring of people with TMD and assist clinical decision making.

INTRODUCTION:An increasing number of clinical studies involving a range of chronic pain conditions report widespread mechanical pressure pain hypersensitivity, which is commonly interpreted as resulting from central sensitization (CS). Secondary hyperalgesia (increased pinprick sensitivity surrounding the site of injury) is considered to be a manifestation of CS. However, it has not been rigorously tested whether CS induced by peripheral nociceptive input involves widespread mechanical pressure pain hypersensitivity. OBJECTIVES:The aim of this study was to assess whether high-frequency electrical stimulation (HFS), which induces a robust secondary hyperalgesia, also induces a widespread decrease of pressure pain thresholds (PPTs). METHODS:We measured PPTs bilaterally on the temples (temporalis muscles), on the legs (tibialis anterior muscles), and on the ventral forearm (flexor carpi radialis muscles) before, 20 minutes after, and 45 minutes after applying HFS on the ventral forearm of sixteen healthy young volunteers. To evaluate the presence of secondary hyperalgesia, mechanical pinprick sensitivity was assessed on the skin surrounding the site where HFS was applied and also on the contralateral arm. RESULTS:HFS induced a significant increase in mechanical pinprick sensitivity on the HFS-treated arm. However, HFS did not decrease PPTs neither in the area of increased pinprick sensitivity nor at more distant sites. CONCLUSION:This study provides no evidence for the hypothesis that CS, induced after intense activation of skin nociceptors, involves a widespread decrease of PPTs.